Fluxes play an important role in solder-joining electronic components, such as semiconductor devices, onto printed circuit cards or printed circuit boards (PCBs). Flux is used in a process of flip-chip joining to a substrate that has ball grid arrays (BGA) or land grid arrays (LGA). In a typical process, by way of example, flux is applied onto a substrate followed by placing a chip onto the flux-applied substrate. Then, the chip-substrate module goes through a reflow process at a high temperature so as to make solder connections. The subsequently formed flux residue is cleaned (for example, with water) followed by drying the module. An underfill material is introduced into the gap between the chip and the substrate to maintain the integrity of the flip-chip package.
As the density of Controlled Collapse Chip Connection (C4) arrays and the chip size increase, the joining process sometimes produces non-wets at a corner of the large chip due to the smaller C4 size and the larger warpage of a substrate. It also becomes more difficult to clean flux residue, formed during flip-chip joining, out of the narrow chip-substrate gap of the large chip package.
Non-wets which make electrical open should be avoided, and flux residue often causes delamination between underfill and chip or between underfill and substrate, resulting in failure of flip-chip packages. As the size of solder balls in a chip decreases, slight movement of an aligned chip-laminate module during a reflow process can cause non-wets, because a typical high-throughput reflow tool tends to vibrate. Such non-wets can increase in the case of multi-chip modules.
However, after joining, left-over flux and by-products of the reaction between flux and solders need to be cleaned, preferably with a low cost and environment friendly method because cleaning with organic solvent is not only harmful to human beings and the environment but also expensive, in regards to both the material itself and the waste treatment process. Therefore, it would be desirable to develop a flux that has sufficient tackiness while the flux residue can be cleaned with water. Another type of flux residue includes organic polymers produced from flux molecules during the high temperature reflow in a modern forced convection reflow furnace with strong N2 gas flow as such a furnace is needed for manufacturing advanced semiconductor packages. The organic polymers cannot be dissolved in water if their molecular weight is high. Thus, there is a need that exists in such approaches to use a certain component of flux with low molecular weight so as not to form insoluble polymers even in the modern forced convection furnace with strong N2 gas flow.
Many existing fluxes in the industry, however, provide an inadequate joining capability in case of lead-free solders, give non-wets at the corner of a chip, leave considerable flux residue including organic polymers onto chip, C4 and substrate surfaces after cleaning, diffuse into the substrate outer layer, and/or cause chip movement during reflow.
By way of example, existing fluxes include disadvantageous aspects such as not providing perfect solder joining, resulting in a failure of the semiconductor package, not providing enough tackiness or viscosity, as well as often leaving polymer, tin oxide and/or organotin residues after reflow that cannot be cleaned with water.
Accordingly, there is a need for soldering flux compositions that can effectively manufacture the modern and high-performance semiconductor packages used for computers, communication devices, home electronics, game consoles, audio/video equipments, automobiles, etc.